Helium vs. hydrogen as a carrier gas in capillary Gas Chromatography

After the expense of a new gas chromatograph, the last thing any chemist wants to see is a big smoking hole in the laboratory where the GC once stood because the wrong choice of carrier gas was made.

Selecting a carrier gas is one of the most important parameters that must be decided upon in the method development phase. The decision is normally based on the literature study or the application notes from the column supplier. There are also safety and financial considerations that influence the decision.

The detector of choice will influence the decision, as a Mass Selective Detector or Pulsed Discharge Helium Ionisation Detector will use helium. If one is to look at the other detectors, for instance Thermal Conductivity Detectors, hydrogen offers a slight advantage on sensitivity. Hydrogen will have a higher velocity through the column over helium, decreasing the retention time by up to 25% in some columns for some analytes.

Hydrogen is flammable over 4% volume in air and this must be considered in the choice, as Gas Chromatographs operate with a range voltages and electrical energies to ignite a hydrogen atmosphere in or around the GC.

If safety is to be considered, the cost of helium vs. hydrogen is negligible as the cost of the alternative cannot be determined. Purity of the hydrogen from a Hydrogen Generator is also offered as a point when carrier gases are decided upon. Hydrogen from a generator is normally 99.9999% pure while most gas suppliers in South Africa have helium at 99.999% purity readily available. This can be overcome by installing a rare gas purifier inline that will purify the helium to better than 99.9999% purity.